The present invention relates to a shading system, particularly for regulating the solar heat gain from the sun and particularly relates to a passive, seasonally selective shading system for limiting solar heat gain in the summer and enabling solar heat gain in the winter, while affording adequate visibility.
As well known, the orientation of windows vis-a-vis the sun has substantial impact on the heat gain within a building. For example, windows having substantial east and west exposures cause significant heat gains within the building during summertime. On southern exposures, the heat gain is usually less because the sun is higher. Such heat gain substantially increases energy costs for air conditioning at lower latitudes. Many different systems have been proposed and constructed to alleviate this problem, including both active and passive systems.
Active systems typically include movable shading systems for shading the interior of the building from the sunlight in order to minimize the heat gain, particularly during the summer and early morning and late afternoon hours. Such conventional active systems comprise movable shades, shutters, blinds and the like. These systems, however, disadvantageously require a high degree of user interaction. While certain of these systems can be and are automated with improved effectiveness, automated systems are costly. All such systems also share the drawback of closing off the view, reducing visibility along with the heat gain.
Certain shading systems may be active or passive. For example, vertical or horizontal louvers may be employed, either as a fixed part of the building or movable to vary the shading effect in accordance with the time of day. On south orientations, where the sun reaches its highest point in the sky, horizontally positioned shade devices on such southern exposed windows provide a reasonable shading effect from the sun's most intense heat. Thus, active or passive horizontally oriented louvers, slats or blinds are reasonably effective. Overhangs on buildings are also effective but oftentimes impractical and costly, e.g., in large office-type buildings. On east and west orientations, passive horizontal shading elements, such as louvers, lose their effectiveness because the sun is lower in the sky in these directions. Vertically placed shading elements preserve some natural light, while blocking out late morning or early afternoon sun in the summer. However, the sun's position relative to the horizon shifts with the seasons, i.e., it rises and sets at a more southerly position during the winter and a more northerly position in the summer. In-between sunrise and sunset, the path of the summer sun passes more directly overhead. Consequently, vertical louvers on west orientations won't block the summer's mid-afternoon sun but will block almost all of the winter sun on east orientations when solar heating is most desirable.
Passive methods of limiting the solar heat gain, particularly in the summertime, also include use of tints, screens or films on or between insulating glass. Spectrally selective films block out the sun's heat-producing infrared rays, while admitting the light. However, these systems only block a portion of the direct rays of the sun in the summertime and cannot discriminate between seasons, depriving the building of beneficial solar heating during the winter.
A further method of minimizing heat gain in the summertime is to minimize or avoid placing windows on the east and west sides of the building altogether. Conventional thinking is to minimize the number of windows on the east or west sides of the building because it is very difficult to shade those sides. However, this solution inhibits the desired solar heat gain in the wintertime and also contributes to a lack of view and oftentimes ventilation.
Further, conventional shading systems typically employ opaque elements having either a horizontal or vertical orientation to block out the sun. By a horizontal orientation is meant that the opaque members lie in a plane parallel to a horizontal plane passing through the building site, i.e., tangent to the spherical earth at the building site. Vertical orientation, of course, is a line or plane perpendicular to the horizontal plane. It will be appreciated that where shading elements have a horizontal orientation in a south-facing wall of a building, that orientation prevents substantial heat gain and effects shading in the summertime without substantially limiting visibility. However, the walls of the building having east and west exposures and provided, for example, with similar horizontally oriented shading elements is not taken into account. Consequently, there is a substantial need for a passive seasonally selective system for limiting solar heat gain in the summer and enabling solar heat gain in the winter.